My Best Friend's Girlfriend
by KaterinaLuciano
Summary: Ariana Snape, Severus Snape's younger sister, had been in a serious relationship with Sirius Black before he was imprisoned in Azkaban. Remus Lupin looked after her when her life fell apart. Now Sirius is back and Remus doesn't know how to deal with their reunion...
1. Chapter 1

**Chapter 1 – What was once**

Ariana Snape and Sirius Black were at Hogwarts around the same time. He was a seventh year and she a fifth year when they found themselves entwined in an empty classroom halfway through a Quidditch victory celebration.

Sirius was a sought-after charmer, a living legend for all the ridiculous pranks he and the Marauders pulled. She was Ariana Snape, the younger sister of Severus Snape, a.k.a. Snivellus to the Gryffindors. She was the freak of the family, much like Sirius, the first Gryffindor from a decidedly Slytherin family. When she was sorted into the Lion's house her brother became more distant and she made friends quickly, all who were Slytherin-bashers.

Ariana had the same black eyes and frail build as Severus, but her eyes were more like glittering onyx's that shone with a life-energy their father managed to beat out of Severus many years ago. She was not beaten often by her father, as Severus was, but Tobias did hurt her in other ways, he did things to her that he could not, would not, do to his boy. Ariana knew her father was a piece of shit and relished in every day she spent away from her miserable home. Ariana also did not inherit the hooked nose and had an acceptable, if slightly larger than she would have liked, nose. Her skin was also pale, but not as pallid as her brother's. She spent many of her hours outside, soaking up the sun, when it paid England the courtesy of showing its face. Her hair was also pitch black, but was never lank after her initial arrival at Hogwarts. Her fellow dormers taught her how to treat her hair properly and Diane Baker asked her mother, the owner of a Bewitching Waves, the most prestigious salon in wizarding England, to send Ariana some volume spray. Her hair was always a straight and sleek curtain that she loved to play with and toss over her thin shoulders.

The most important difference between Ariana and Severus was their personalities. Ariana was outgoing and jovial, while Severus was the complete opposite. Perhaps Sirius thought he could do Snivellus the ultimate injustice by soiling his sister. Ariana would have never come close to her big brother's tormentors if she wasn't drunk off her face on fire whiskey, but she did. She had her first pleasurable sexual experience with a man that only caused her once beloved brother pain. The man who was probably only using her, taught her how two people's bodies can fit perfectly and grant each other great pleasure. When they were done they started talking and didn't stop until the morning's light. Something in them seemed to pull them towards each other. They started seeing each other in secret and when he finished school at 18, when she was only 16 years old she moved in with him, vowing never again to set foot in her abusive father's house. Sirius had left his parents' house at sixteen, staying with the Potters mostly, but now he had his own small flat near Diagon Alley.

She knew Severus was lost, a follower to the Dark Lord. He was the darkness, so she needed to be the light. Sirius and Adriana partied like they were the king and queen of the world that summer, until it was time for her to go back to Hogwarts. It was hard for her to leave Sirius after spending every waking moment with him, but he wanted her to do her N.E.W.T.S. and pass them with flying colours. Ariana was not one bit dumber than her brother, if maybe a little more lazy, but she was the academic star of her year, and with Lily Evans gone, the brightest mind at Hogwarts. Sirius said he would get a job so they could stop living off money and jewels he stole from his parents.

Ariana finished her N.E.W.T.S. with a full set of Outstanding's, even in Arithmancy, a terrifically difficult subject. They celebrated with good old Muggle champagne and by shagging on every surface in their flat. Within the month she secured an apprenticeship with Barabbas Dragonsteele, the pre-eminent charm-conceiver of the time. They were so blissfully happy in the summer of 1981, even though it was wartime and they did not see much of each other. The love of danger which brought them together made their time together all the more passionate.

31 October 1981 was the worst evening of Ariana's short life. James and Lily Potter were killed by the Dark Lord and Sirius was to blame. A boy was orphaned and the Light Side lost two of its greatest defenders by her lover's hand.

"You can place a Slytherin in Gryffindor, but you can never take the Slytherin out of him."

Off-hand words spoken by a barmaid haunted Ariana until she tried to take her own life. She thought she would also turn on Dumbledore and all he stood for, because of her heritage. She tried to hang herself from her and Sirius' four-poster bed, but the wood had broken under her weight and Remus Lupin found her lying on the floor unconscious before she could try her luck a second time.

Remus became her guardian angel; he was what kept her alive through the first year without Sirius. She became more active in the order of the Phoenix, even though she had only just turned 19. The risk was less now the Dark Lord was gone, but they still had rogue Death Eaters to calm down. She never knew why Remus cared so much about her staying alive, whether it was because he learned to like her in the numerous hours she and the Marauders spent together, if she reminded him of Sirius or if he was simply a good person. She lost her apprenticeship and got a job at a bookstore in Diagon Alley. She learned to live with the pain of another man breaking her trust and she and Lupin would spend many bittersweet days together discussing books and the future of the wizarding world.


	2. Chapter 2

**Chapter 2 – What now remains**

June 1995

A loud crack sounded behind Ariana's back. She whirled around, wand at the ready to maim a potential threat, but it's just Nymphadora Tonks.

"Tonks, could you not scare me like that?"

One look at Tonks' colourless face warned Ariana that her world was about to collapse around her.

"Ariana... Sirius is at the Burrow... I know you two have history..."

She couldn't hear Tonks complete her sentence; she only heard a loud ringing, as if a bomb had just gone off nearby. A metaphorical bomb did just drop. Sirius Black, the convict who sold out his best friends for the Dark Lord, was back. Sirius Black, the man she had once loved and planned on spending the rest of her life with, was at the Burrow.

Tonks' voice came fading back in.

"Oi, Arry, are you alright?"

Ariana doubled over and emptied the contents of her stomach onto the bookshop's floor.

Tonks swore loudly and pulled out her wand to clean the mess. Ariana wiped her mouth with the back of her wrist and hoarsely mumbled, "I need to go."

With a loud crack she was gone, leaving Tonks to notify the store's owner of the unmanned shop.

Ariana appeared as close to the Burrow as possible and, as if in a trance, made her way through all the wards on the Order's headquarters. She swung open the door and looked straight at the face of Sirius Black.

"You bastard!"

Ariana flung herself with all her might onto the emaciated man. She was screaming and biting and hitting, doing her best to cause as much physical damage as she possibly could. She was hauled off him by familiar arms. She felt Remus' warm breath on her ear as he pleaded with her to calm down, to hear Sirius out...

"Why are you defending him, Remus? He killed Lily and James! He is a traitor! He is a filthy bastard not deserving of life!"

Ariana aimed one last kick at Sirius before completely collapsing into Remus' chest, sobbing hysterically. She moaned as if in physical pain. Her face contorted in agony, all her emotions that she hid deep within herself in 1981 came bubbling to the surface. The betrayal felt fresh and her chest hurt as if she was having a heart attack. Remus slipped his left arm underneath her knees and carried her to the living room. He sat down with Ariana wailing and weeping in his lap. He motioned for Sirius to sit across from them.

Remus saw Sirius' expression: his face was also contorted. Remus saw that his love for Ariana had not died in the almost fourteen years since they had seen each other. Ariana clearly still had strong feelings toward Sirius, be it hatred or love.

For the next two hours Remus and Ariana listened to the tale of Sirius Black's unfair imprisonment. Peter Pettigrew was the real traitor and Sirius was the one who was persecuted. The tale of his escape was extraordinary to say the least. The hippogryph Buckbeak was somewhere in 12 Grimmauld place, the place where Sirius would now be hiding out. Ariana remembered that was the name of Sirius' parents' house and as she vowed never to return to her father's home, he vowed never to return there.

On shaky legs Ariana arose from her spot curled up on top of Remus Lupin.

"I need to talk to you in private," Ariana whispered almost inaudibly, keeping her gaze on the floor and grabbed a hand full of floo powder, stepped into the fireplace and stated, much more clearly, "12 Grimmauld Place".

She stepped out of an extremely dusty fireplace into an even dustier living room. Clearly Sirius had not been here long; there were no wards on the house yet. The whole house seemed terribly dark and dreary. She was struggling to open some curtains when she heard the sound of someone arriving via the fireplace.

Sirius' face was a mask of sadness and regret. He slowly walked to Ariana and she stood perfectly still taking in the man that looked so different to the man she once called her lover. His face was sunken and his hair was matted and long. He had vagrant-looking facial hair and his eyes did not glitter mischievously.

He placed his cold hands on either side of her face.

"I am so, so sorry for what I put you through," Sirius whispered.

Ariana held unblinking eye-contact with him for ten long seconds.

"You know what, fuck it," Ariana said and pulled down Sirius' mouth onto her own.

His lips were dry and his tongue felt almost inexperienced caressing hers. Fourteen years could do a lot to a man, make him old, emaciated and could make him forget even the most primal of his skills. Even though Sirius wasn't nearly as proficient a kisser as he used to be, he was just as passionate.

Sirius pulled Ariana against his bony chest and moaned deeply into her mouth. She felt his hardness pressing into her belly. She quickly divested Sirius of his shirt and started kissing his neck and chest. She nipped at his skin, remembering how he used to like that. Sirius kept moaning and running his hands through her hair. As Ariana was going to undo Sirius' pants, he yanked her up by her shoulders and then picked her up under her bottom and plonked her down on a likely plague-infested couch. She made to stand up from the filthy-looking furniture, but Sirius pushed her down on her stomach.

"I haven't tasted a woman in fourteen years. I'm starving and I'm about to make your pussy my main course," Sirius rasped from between her legs. He pulled down her jeans and panties in one fluid motion. Ariana's eyes rolled back at his words and she thanked Merlin she kept her downstairs neat for her drunken conquests.

Sirius's lapped and sucked on Ariana while she screamed her pleasure until she came undone. With pleasure-blurred eyes she saw him pull off his pants and then felt his weight on her. He entered her in one thrust. He stilled and shuddered and Ariana wrapped her smooth legs around his back. He set them a frantic pace that was doomed to be over quickly. When he came inside of her he yelled her name and rolled off the couch onto the floor, not one bit bothered by the fact that it hurt. He had just had the best sex of his life. Ariana peered down at him.

"Well, I think I just gave you a warm welcome."

"As good as ever, Ariana, maybe even better, have you been practicing without me?" Sirius asked with a wide grin.

Ariana blushed and stammered out that she didn't think he was ever coming back.

"Shhh, I know sweetheart," Sirius soothed her and stroked her sex-hair. "It's okay."

Ariana removed herself from the couch and lied next to Sirius on the floor. She snuggled her head into his chest and sighed.

"Sirius... it's all fine and well you're back, but... what now?"

"I don't know, Snapette, are you willing to take back a wanted convict?"

His use of her old nickname moved something in Ariana. She grasped Sirius' chin firmly in her hand.

"You barge in here, tell me a wild story, completely changing my view of what happened thirteen years ago and now you want me to just invite you back into my life?"

Sirius looked away, mortified that he actually expected the beautiful Ariana to just be there now he was back, to just take him back into her heart. He didn't know if she had a husband and children now, he might have made her an adulteress by this tryst.

"Of course I will take you back; my life has been such a train-wreck since I lost you. I lost my apprenticeship; I work at a bookstore for fuck's sake! I was meant for greater things, but I fucked up, I fucked everything up so badly. Oh, Lord, Padfoot, I failed. I am a failure."

Sirius felt her tears wet his chest.

"I am so sorry for the pain I have caused. From now until my last breath I will try to make it all up to you. You are still young, 32 if I'm correct. You can make something of yourself."

Ariana nuzzled her head into his chest in agreement.


	3. Chapter 3

**Chapter 3 – Putting back the pieces**

Sirius and Ariana had been living in 12 Grimmauld Place for a week. All of the Order members now knew the true story of what happened. Sirius suggested that the Order headquarters be moved to Grimmauld place as it had no other use at the moment. Molly was all too glad, the Burrow was taking too much strain and it was getting dangerous for Arthur, who the Order was pretty sure the Ministry was monitoring. Every day there was a clean-up effort and every night Sirius and Ariana would go to his childhood bed and make love, sometimes multiple times, and lose themselves in each other. It was like discovering each other for the first time. His body was no longer that of a strapping twenty year old and her body was also not what it used to be. She was a little more rounded in the hips and chest and her stomach made a tiny bump. She enjoyed helping Molly feed the masses. There was a big commotion with Harry; he used a Patronus charm to ward off some Dementors in front of his Muggle cousin and had a full scale trial for it. He got off, because it was a truly ridiculous situation, in Ariana's opinion. Sirius and Harry had been bonding and it was quite sad to see all the children off to Hogwarts. Sirius offered Remus permanent board at Grimmauld Place the day everyone left, which he gladly accepted. Ariana felt it was going to be like old times.

...

Ariana woke stark naked on the first day of silence, half covered by Sirius. She disentangled their limbs and slid on some comfortable black panties and pulled on an old white tank top and headed downstairs. She started cracking eggs into a bowl and getting Arthur's newest Muggle-magic fusion set up: a toaster. She was cooking the scrambled eggs when Remus cheerily entered the kitchen.

"Morning, Arry," he greeted sunnily, until he saw what she was wearing and stopped dead in his tracks. Ariana looked over her shoulder and saw his stunned expression.

"What's up, Moony? Don't you like your eggs scrambled?" she joked.

Remus seemed to snap out of it and averted his eyes.

"It's nothing, sorry." He plonked himself down on a kitchen chair facing away from Ariana.

Ariana removed the pan from the stove and walked to the kitchen door and shouted, "Oi, Sirius, you sleepy shit, I have food for you!"

With a big smile Ariana began piling three plates with eggs and toast.

"Moony, I feel obliged to tell you that I am going to feed both of you men until you look less lean, you're making me feel self-conscious," Ariana joked as she presented Remus with his plate of food.

Remus met Ariana's cheerful gaze with serious eyes.

"Trust me, Ariana; you don't need to feel self-conscious about any part of your body."

Ariana's eyes widened as she realised what was wrong.

"Oh, shit, Remus, I didn't realise you had a problem with me walking around like this. I'm such a fool, who walks around half-naked anyway..."

Sirius sauntered into the kitchen and greeted Ariana with a slap on her mostly exposed bum.

"I like you dressed like this," he said, nuzzling her neck.

"Fuck off, Padfoot, I'm making Moony uncomfortable," she said shoving him toward the table.

Remus hid his beetroot face and stuffed some food into his mouth.

"Aw, Moony, really? Has it been long since your last lay?" Sirius asked.

Ariana threw a fork into the back of Sirius' head.

"What the fuck is wrong with you?" she yelled.

"It's an innocent question and if you don't want a spanking for being so naughty I suggest you sit down," Sirius said with an evil grin.

Ariana widened her eyes at him, signalling that he was acting inappropriately, but Sirius ignored her.

They ate in silence for a while and then Remus finally raised his head.

"Merlin, you two were nothing like this when you had a full house. Now you two are walking around half-naked, you're threatening her with spankings and you are both just generally being weird. What is the problem? Should I leave?" Remus looked at Ariana with questioning eyes.

"Oh, no, I'm sorry if we made you feel uncomfortable, I just figured now that the place isn't crawling with Weasleys and all the others, except at meeting times, we could let loose more. You know, like old times. You never used to worry about me not having clothes on," Ariana said wide-eyed.

"Yes, well you were so young then and mostly drunk when you didn't have clothes on; it was all less... weird. Now I know you as an adult who has faced Death Eaters alongside me, not Sirius' lovely young conquest turned girlfriend."

"I resent that," Sirius proclaimed with a mouth full of food. "She was never a conquest, just a drunken mistake." He winked at Ariana and continued stuffing his face.

"That is so disgusting, you pig. If you are going to eat like that, keep your bloody mouth closed!" Ariana rolled her eyes in her particular manner. Her left eye made a full circle, but her right only did an up-down motion. She leaned forward and grasped Remus' wrist, affording him a view of her milky white breasts and one perfect pink nipple.

He stood up so quickly that he knocked his chair over.

"You see that? I could see completely down your shirt! I can't do that! I have spent a decade and a half looking after you like a sister after Sirius was sent to Azkaban, I never once tried to have a look at you. Not when you were so piss-drunk I had to undress you and put you to bed and not when you slept on my chest when you felt over-whelmed. I let you share my bed and everything was completely platonic. I can't take this teasing of your body, I am sorry."

He stood up to leave but Sirius stopped him with a hand to his chest.

"I'm sorry, Remus. "

"You know what? For all it that apology means you can shove it up your arse."

Remus slammed the door behind him and Ariana and Sirius were left looking at each other.


	4. Chapter 4

Remus was just about pulling out his own hair in frustration. The first part of the week he had not paid particular interest to anything as he had his transformation and hid in the Shrieking Shack mostly. The last two days he had discovered a green-eyed monster in him. First, he thought it might have something to do with the wolf in him, but it did not fade. Every time Sirius pulled Ariana to his chest and she looked at him with the utmost love, he felt a dagger through his chest. When they send each other up it was like seeing them as they were in their seventh year.

Remus was jealous of Sirius. He had barged in on their lives and turned everything upside down. He forced the Order to rewrite their history books. Most of all, he made Ariana whole again. She was positively radiant. He could never make her as happy. He was just a poor replacement for the real deal. Sirius was always the one who got attention, who got the girls.

This might have been fine if not for the fact that they were so public about their happiness. They shagged constantly, and like old times, they wanted to do it on every possible surface in Grimmauld Place. Fred and George Weasley had walked in on them as they were busy on the kitchen counter. They were sworrn to secrecy, but Remus had overheard the twins telling Ron about it. A simple Scourgio would clean any bodily residue they might have left behind, but the thought of it lingers in Remus'mind.

When Remus saw Ariana standing there in her flimsy black knickers, not quite covering her firm white ass, he was embarrassed at the reaction of his body. He felt aroused and then guilty at feeling that way over a woman that trusted him as a friend. When she leant over the table and he saw that one perfect, still perky breast it was the last straw. He had knocked over his chair, yelled like a man with no hold on his emotions and was now seated at the Hog's Head working through his third fire whiskey.

Ariana gaped at Sirius.

"What have we done?"

With those words she promptly burst into tears.

Sirius stood up to walk to her and put his arm around her.

"I think we might have been a tad insensitive to Moony. We shouldn't flaunt our happiness in front of someone with so little to be happy about." Sirius kissed the top of her head.

"I thought he would be happy for me! He is my best friend, Sirius!" Ariana wailed.

Sirius picked up Ariana out of her chair and carried her crying towards their bed. He neatly laid her down and she curled up into a ball. She looked so small and Sirius realised what his love's life had been like. An abusive father, a brother fighting for the wrong side, the death of two of her closest friends, her lover turned murderer. A string of disappointments. Now her brother was fighting for the light side, but was broken beyond repair. And he just turns up out of the blue. Turning her life upside down. He was an unwanted part of Ariana and Remus' life. They had learned how to get along without him.

"Sirius…"Ariana moaned softly. She held he arms straight out to Sirius. He softly kissed her, tasting her salty tears on her lips. She clung to him like a lifeline. He could feel she was still crying, by her small twitches and irregular breathing. He kissed her soft neck.

"Moony will deal with his feelings, but nothing and no one will ever make me give you up again," Sirius said into Ariana's hair.

Ariana curled herself along his body and nuzzled her face into the crook of his neck. "Never."

Sirius sighed and grasped her chin so he could tilt her head up to meet his eyes.

"So what are we going to do about Moony?" he murmured.

Ariana wiped her tears away with her knuckles, making her look like a child. She shook her head and shrugged her shoulders. Sirius swore under his breath, because he had no ideas either.


End file.
